Aircraft electrical systems generate, regulate and distribute power throughout an aircraft, and it is essential that power is reliably maintained to these electrical systems. Often, auxiliary power units (APUs) are used to provide power to electrical systems within an aircraft when main engines are not running. Most APUs are relatively small turbines that use electrical starting power. Once the APU is running, it can function as an electrical generator for the aircraft.
Most APUs use capacitive discharge ignition systems which involves initially charging a high voltage capacitor, often using a charging circuit such as an ignition exciter unit. The ignition exciter unit includes a relatively large input capacitor, which results in an inrush current when the ignition system is first powered on. Because of the high inrush current, it is difficult to design circuit protection that does not interrupt the ignition exciter unit as a result of the inrush current yet reacts quickly to overload or short circuit conditions.
High-side driver circuits have been developed for reliably driving ignition systems used with aircraft turbines. However, these high-side drivers are based on discrete component topologies and often require thirty or more electrical components, reducing component density and increasing assembly costs. While integrated circuits have been developed for lower power applications, such devices fall short of being able to reliably drive an ignition exciter unit, mainly due to their inability to supply the high inrush-current drawn by the typical ignition exciter unit.